The demands on wireless communication capabilities in today's society are increasing rapidly. In particular, fast and easily accessible communication is desired through hand-held devices over large areas. It is particularly challenging to achieve such communication for mobile devices which are moving, e.g. when moving over large distances with poor network coverage or when affected by unknown sources of noise interrupting a signal for communication, such as clients moving on trains. In particular, if a client, being for example a mobile phone, moves over large areas the client has to connect to several base stations in order to maintain a sufficient connection for communication.
The mobile nature of a client with respect to the base stations may introduce several potential sources of communication performance degradation. Such sources may derive from complex terrain, competition for available channels, or the source may be an unknown source of noise related to e.g. radio-frequency interference.
At the same time, there is today an increasing demand from passengers to be able to communicate through mobile phones and other handheld terminals when travelling on e.g. trains, and also to be able to get access to the Internet with laptops, PDAs etc. Further, with the new smartphones, and the way these are used, with e.g. continuously operating applications, many phones are active at all times, meaning that many handovers are required when the train moves. Even though this problem is common for all moving vehicles, it is especially pronounced for vehicles moving at high speed, such as trains.
To this end, solutions using internal networks within the trains, and connection to external network through routers, have been developed. Further, EP 1 175 757 by the same applicant describes a method whereby many of the weaknesses resulting from wireless communication may be overcome through the concurrent use of multiple links, including both wired and wireless technologies. However, the aforementioned solution is often insufficient to obtain an optimal transmission performance. Trains and other moving vehicles often pass through areas with bad radio coverage, and present solutions are often unable to handle the required traffic.
At the same time, there has been a trend towards trains moving at higher and higher speed, such as TGV and the like, and also towards larger and larger trains. The higher speed provides increase strain on the wireless communication. Further, larger trains, such as double decker or bi-level trains; provide less space for antennas on the roof. The available space is often very limited, or even non-existent. Further, high-voltage cables are often provided along the train roof, making the possible placement of antennas even more restricted. To this end, antennas are often confined to less suitable locations, such as in between carriages, at locations having no line-of-sight at both sides of the train, etc. This degrades the antenna performance, and hence the overall performance of the wireless communication system.
There is therefore a need for an improved wireless communication system for moving vehicles, and in particular trains, which provides improved radio communication performance and an improved communication system.